a. Field of the Invention.
The invention relates to apparatus used for centering rotating data storage media and more particularly, to a spindle for centering a disk hub on the spindle.
b. Prior Art.
Disk recording media are used in the computer industry for storage of large amounts of data. The recording media may contain millions of bytes of data which are accessible to the computer by means of a transducer or reading head which scans the data as it rotates at high speed relative to the recording head. The recording medium may be a ferromagnetic material having magnetic characteristics which make it suitable for reading or may have optical characteristics which make it suitable for reading, or may have still other characteristics. However, in most instances the medium itself is somewhat fragile and although it typically rotates at high speed, the medium itself is not attached to a spindle. Rather, the medium is mechanically attached to and supported by a hub which in turn is connected to a spindle or other spinner mechanism of a motor.
In U.S. Pat. No. 4,166,622 granted Sept. 4, 1979 E. Rager discloses a collar construction for a disk hub in which the interior of the collar is adapted with a plurality of cylinders having a peripheral shape mating with portions of the spindle to which the hub is fit. The cylinders have longitudinal slots extending partially therethrough allowing compression of the cylinders when in contact with a spindle. When the cylinders are pressed into the interior of the collar, the collar may be used for centering a disk on a spindle.
In U.S. Pat. No. 4,171,531 issued Oct. 16, 1979 R. Grapes and D. Watson disclose a centering device wherein a plurality of upstanding centering fingers are mounted in the spindle so that the fingers may engage a cone which enters the spindle, urging the cone toward a centered relation with the spindle. The cone serves to center a disk.
In U.S. Pat. No. 4,091,454 issued May 23, 1978 Kauffman teaches use of a spindle having outwardly facing fixed ribs. An eccentric multi-lobed triangular center is placed over the spindle with apexes of the triangle being placed over the ribs. The hub is then twisted with the ribs then centering the hub.
One class of hubs is adapted for mounting on a rotating spindle by means of a special collar in the interior of the hub for centering the hub with respect to a spindle which fits within the collar. The hub must be accurately centered because data reading and writing transducers rely on the concentricity of the data tracks. While adjustments of the transducers are made by servos, the data tracks are centered at the geometric center of a hub which should have its geometric center coincide with the geometric center of a spindle, usually driven by a motor.
In order to fit on a spindle, the inside diameter of a hub must be slightly greater than the outside diameter of a spindle. In order to make sure that the hub is centered on the spindle, a compression member is usually provided such that the compression member, when attached to the inside diameter of the hub actually causes the hub to have a smaller inside diameter than the outside diameter of the spindle. However, when the hub is placed over the spindle, the compression member compresses and the hub is thereby centered on the spindle.
A widely used prior art hub is illustrated in FIG. 1 of the drawings. A portion of an annular hub 11 is shown, having an annular collar 13 in its interior, for placement on a spindle. The geometric center of the collar coincides with the central geometric axis, A, of hub 11 and a spindle on which the hub is placed. Collar 13 is usually machined out of metal and is tightly pressed into place in the center of a hub.
The collar 13 has an inside surface 15 and an outside surface 17. The inside and outside surfaces are in fact walls separated by a circular groove 16, which extends part of the way from the top to the bottom of the collar. The bottom of the collar supports the inner and outer walls. The inside surface 15 is interrupted at intervals by short wall portions 19, 21, 23 which project inwardly more than the remainder of the inside wall. The wall portions 19, 21, 23 form fingers which compressibly contact the exterior of a spindle for accurate centering of a hub on the spindle. It should be noted that the fingers do not transfer mechanical energy to or from the hub for spinning. Such energy is transferred by other means, such as by lugs or bolts which do not influence alignment of the hub with respect to the spindle.
With reference to FIG. 2, the manner of using the prior art collar of FIG. 1 is illustrated. The collar 13 within hub 11 is turned upside down relative to FIG. 1 and the hub 11 is placed over the spindle 25. The spindle has a cantilever section 27 with a support rim 29 with which the hub 11 makes contact by means of pads 31 and 33. Bolts may also extend into rim 29 between the pads 31 and 33 for mechanically securing the hub 11 to spindle 25, so that rotary motion from the spindle can be transferred to the hub. It may be seen that the top of the spindle tapers inwardly and that the only contact made between the center shaft of the spindle and the hub is made with the centering collar 13.
However, as can be seen from FIG. 1 it is quite difficult to manufacture the collar shown. The inside wall has different circular diameters. The first and greatest diameter is formed by the main portion of the inside surface 15 of the wall, while other, lesser diameters are defined by the portion of fingers 19, 21, 23 facing the axis of rotation. The upper portion of each of the fingers 19, 21, 23 has a diameter approximately one or two thousandths of an inch less than the lower portion thereof, which in turn has a diameter approximately twenty thousandths of an inch less than the main wall portion of inside surface 15. The construction of the collar 13 requires intricate machining, such that most of the cost of the hub is represented by the collar 13.
An object of the invention is to devise a simplified construction for centering a disk hub on a spindle which is characterized by lower cost compared to prior art collar and spindle constructions.